In the field of non-impact printing, the most common types of printers have been the thermal printer and the ink jet printer. When the performance of a non-impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been the control of the printing operation. As is well-known, the impact operation depends upon the movement of impact members, such as print hammers or wires or the like, which are typically moved by means of an electromechanical system and which may, in certain applications, enable a more precise control of the impact members.
The advent of non-impact printing, as in the case of thermal printing, brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing, in at least one form thereof, must deal with rapid starting and stopping movement of the ink fluid from a supply of the fluid. In each case of non-impact printing, the precise control of the thermal elements and of the ink droplets is necessary to provide for both correct and high-speed printing.
In the matter of ink jet printing, it is extremely important that the control of the ink droplets be both precise and accurate from the time of formation of the droplets to depositing of such droplets on paper or like record media and to make certain that a clean printed character results from the ink droplets. While the method of printing with ink droplets may be performed in either a continuous manner or in a demand pulse manner, the latter type method and operation is disclosed and is preferred in the present application when applying the features of the present invention. The drive means for the ink droplets is generally in the form of a well-known crystal or piezoelectric type element to provide the high-speed operation for ejecting the ink through the nozzle while allowing time between droplets for proper operation. The ink nozzle construction must be of a nature to permit fast and clean ejection of ink droplets from the print head.
In the ink jet printer, the print head structure may be a multiple nozzle type with the nozzles aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in line manner.
Alternatively, the printer structure may include a plurality of equally-spaced, horizontally-aligned, single nozzle print heads which are caused to be moved in back-and-forth manner to print successive lines of dots in making up the lines of characters. In this latter arrangement, the drive elements or transducers are individually supported along a line of printing.
In a still different structure, the nozzles are spaced in both horizontal and vertical directions, and the vertical distance between centers of the ink jets equals the desired vertical distance between one dot and the next adjacent dot above or below the one dot on the paper. The horizontal distance is chosen to be as small as mechanically convenient without causing interference between the actuators, reservoirs, and feed tubes associated with the individual jets. The axes of all jets are aligned approximately parallel to each other and approximately perpendicular to the paper. Thus, if all nozzles were simultaneously actuated, a sloped or slanted row of dots would appear on the paper and show the dots spaced both horizontally and vertically. In order to produce a useful result consisting of dots arranged as characters, it is necessary to sweep the ink jet head array back and forth across the paper, and actuate each individual nozzle separately when it is properly located to lay down a dot in the desired position. A vertical row of dots is created by sequentially actuating the nozzles rather than simultaneous actuation, the latter being the preferred practice in the more common nozzle arrangements.
A further observation in ink jet printers is that previous and current designs for drop-on-demand ink jet print heads are sensitive to the ingestion of air into or the presence of air in the supply of ink. Even a small air bubble can interrupt or fault the performance of transducers or like devices that expel ink droplets from a nozzle by means of pressure pulses created within an ink-filled chamber or channel.
The use of a fast-acting valve to control the flow of ink to a single ink jet printing nozzle is known in specific applications, but in certain cases, the concept and heretofore-known structure has been considered costly and impractical. Additionally, the supply of ink to a plurality of ink jet nozzles may be controlled by means of a single control device wherein the nozzles are connected to a common manifold and ink droplet ejection is accomplished by momentarily increasing the pressure in the manifold.
After the droplets of ink have been ejected from the nozzles, the ink is replenished thereat from a remote supply by the capillary action of the meniscus at the end of the nozzle. In certain of the control devices and arrangements, it has been found that some difficulties arise from the capillary action refill or replenish process and there are adverse effects on the performance and reliability of such printers.
In normal operation of an ink jet print head, it is well-known that a negative meniscus of ink should be maintained at the nozzle, that the relative levels of ink in the various parts or areas of the system have an effect on the printing operation, and further, that the movement of the several printer elements affects the flow of ink during the printing cycle.
Representative documentation in the field of ink control means for ink jet printers includes U.S. Pat. No. 3,805,276, issued to H. Ishii on Apr. 16, 1974, which discloses ink jet recording apparatus having an ink pump and wherein a valve is associated with a supplementary ink holder, a temporary ink receptacle and the nozzle in an arrangement for removal of air from the ink during a non-printing period.
U.S. Pat. No. 4,038,667, issued to S. L. Hou et al. on July 26, 1977, discloses a pressurized ink jet supply system for an array of ink jets wherein an on-off valve is interposed in the conduit between the ink reservoir and the nozzles, and a second valve is positioned in a line between a second source of ink under pressure and the conduit in an arrangement to reprime for printing operation or to purge the system.
U.S. Pat. No. 4,084,165, issued to B. Skafvenstedt on Apr. 11, 1978, discloses a fluid jet writing system having a pump, a reservoir and a valve along with a comparator in the hydraulic circuit for maintaining a predetermined fluid pressure in the fluid supply line between the pump and the valve by controlling the operation of the pump.
U.S. Pat. No. 4,095,237, issued to J. R. Amberntsson et al. on June 13, 1978, discloses an ink jet print head which has an ink reservoir that follows the movement of the print head, and includes a filter in the liquid flow path.
U.S. Pat. No. 4,126,868, issued to W. Kirner on Nov. 21, 1978, discloses an air venting device for ink supply systems wherein a reservoir supplies ink to a manifold or capillary tube and then to the nozzles. An air bleed passageway communicating with the reservoir has a predetermined small diameter to produce a capillary effect.
U.S. Pat. No. 4,152,710, issued to M. Matsuba et al. on May 1, 1979, discloses an electromagnetic cross valve provided for selectively connecting a nozzle with an ink liquid supply conduit and an ink liquid drain conduit for control of ink level in the system.
U.S. Pat. No. 4,215,350, issued to K. H. Mielke et al. on July 29, 1980, discloses ink jet printing apparatus with different ink jet spacings wherein each of the nozzles is connected through a solenoid valve to an ink supply and each valve is controlled by a pattern generator which timely selects valves and causes simultaneous pulses to be supplied to the selected valves.
U.S. Pat. No. 4,287,523, issued to J. E. Thomas et al. on Sept. 1, 1981, discloses a ball valve for a rotary ink jet printer and positioned in an arrangement to control the ink flow from one chamber to another chamber.
U.S. Pat. No. 4,323,907, issued to V. J. Italiano on Apr. 6, 1982, discloses a ball valve which is affected by inertia to open and close an ink line from a reservoir to a plurality of ink jet heads.
And, United States application, Ser. No. 342,256, filed Jan. 25, 1982, and assigned to the same assignee as the present invention, discloses a ball valve actuated in electromagnetic manner to cause droplets of ink to be ejected onto record media.